METHOD FOR PRODUCING LOW YIELD RATIO HIGH TENSILE STRENGTH STEEL

• Main Authors: MAEDA HISAFUMI, OMORI TOSHIMICHI
• Format: Patent
• Language: English
• Published: 21.08.2001
• Edition: 7
• Subjects: ALLOYS; CHEMISTRY; FERROUS OR NON-FERROUS ALLOYS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUSMETALS OR ALLOYS; MAKING METAL MALLEABLE BY DECARBURISATION, TEMPERING OR OTHERTREATMENTS; MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVINGMATERIAL; METALLURGY; METALLURGY OF IRON; MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; PERFORMING OPERATIONS; PUNCHING METAL; ROLLING OF METAL; TRANSPORTING; TREATMENT OF ALLOYS OR NON-FERROUS METALS

PROBLEM TO BE SOLVED: To provide a method for producing low yield ratio high tensile strength steel which is excellent in the efficiency of rolling and heat treatment and whose tensile strength lies in a range of 590 N/mm2. SOLUTION: In this method for producing low yield ratio high tensile strength steel which is excellent in weld cracking sensitivity and whose tensile strength lies in a range of 590 N/mm2, steel containing, by mass, 0.06 to 0.11% C, 0.01 to 0.4% Si, 0.5 to 1.6% Mn, 0.01 to 0.1% Al, 0.1 to 1.0% Mo, 0.01 to 0.1% V, <0.005% Ti, <0.0003% B, and the balance being substantially Fe with inevitable impurities and having a P cm value of <=0.22 is heated at 1,000 to 1,250 deg.C is subjected cumulative rolling reduction of >=20% at a steel surface temperature of 950 deg.C to Ar3 in accordance with desired characteristics at the time of rolling, is air-cooled after the rolling, is subsequently reheated to the two phase region of Ac1 to Ac3, is thereafter quenched and is then subjected to tempering treatment at the Ac1 temperature or below: wherein, P cm=C+Si/30+Mn/20+Ni/60+Cr/20/Mo/15+V/10+5B.